Harav Moshe Feinstein zt”l, however, finds this ruling most difficult to accept (Iggros Moshe, Yoreh De’oh 4:13). It is implausible, he reasons, that mere slightness of the hand can invoke a Torah prohibition. Surely, he continues, we find that individuals gifted with wondrous powers are entirely permitted to make use of them, even if others will inevitably think that supernatural forces are at work. Shimshon could therefore make use of his supernatural strength against the Philistines, and Naftali could run at his incredible speed to fetch the document of proof (for the sale of Me’aras Hamachpeilah to Yaakov) from Egypt.
The same, states Harav Feinstein, is true of slightness of the hand with regard to magic tricks. Furthermore, while Shach cites a ruling of Rema (responsa 67) to back the ruling of Bach, Iggros Moshe uses the same reponsa to refute Bach, demonstrating that there is no prohibition on deceiving the eyes through natural means alone. Harav Feinstein maintains this to be true even according to Rambam.
Though wary of disputing those who prohibit it, Iggros Moshe thus concludes that were he asked, he would attempt to shy away from answering the question; were he unsuccessful, he would permit the performance of “magic tricks,” as long as the magician declares that all his acts are perfectly natural, and involve no supernatural phenomena.
This stance is echoed by Radbaz (Metzudot David 61), who maintains that the Torah only prohibits true acts of sorcery, and not deceptive acts that rely on purely natural phenomena. In a responsa (1695), Radvaz accordingly rules that other than “theft of the heart,” there is no prohibition concerning such magic tricks. The problem of “theft of the heart” is of course solved by Iggros Moshe’s instruction that the audience be informed in advance that all tricks employ nothing more than natural phenomena.
Rav Betzalel Stern (Betzel Hachochmah 4:13), likewise cites several Rishonim who imply that the prohibition of deception of the eye applies solely to the use of supernatural powers.
(Radvaz does, however, concede that the opinion of the Rambam is to prohibit such tricks, but attributes this to the general opinion of the Rambam who maintains that all witchcraft and “supernatural forces” are false, and should not be reckoned with at all (see Bi’ur Hagra, Yoreh De’oh 179:13). The truth, says Radvaz, is that there are many types of supernatural forces, which are the various forms of sorcery prohibited by the Torah. Slight of the hands, however, and other natural phenomena, are permitted.)